This invention relates to improvements in runway approach procedures using the localizer alone. During the decade of the 1940's, when the ILS (Instrument Landing System) came into being, that instrument, called the “crosspointer,” was designed to display, to the pilot, the deviation from a desired landing path, one needle for left-right (localizer), the other for up-down (glide-slope). ILS is well described by W. E. Jackson in 1959 IRE Transactions and reprinted recently by C. B. Watts, Jr. in INSTRUMENT LANDING SCRAPBOOK available at TRAFFORD.com,
In a later decade, however, when there were some difficulties with installing a proper glide-slope at an airport, it was decided to authorize the use of localizer alone, leaving the one needle not operating (flagged). The desired up-down information was then obtained by using means, such as Altimeter, DME, or Global Positioning System as prescribed in the approach procedure for the particular airport. It is, however, hard to argue that it would not be good to have the glide-slope needle still operating.